Paper PS-ThA7
Investigation of Surface Roughness in III-V Semiconductors After an In Situ Hydrogen Plasma Clean Prior to PEALD

Thursday, October 31, 2013, 4:00 pm, Room 104 C

III-V compound semiconductors, such as GaSb, are attracting widespread attention as an alternative to Si in advanced complementary metal-oxide-semiconductor (CMOS) technologies; their high electron and hole mobilities, as well as relatively narrow bandgaps, makes them particularly well-suited for high-speed, low power applications. However, for high-performance device realization, the quality of the interface between the III-V semiconductor and the gate-oxide is crucial. Most III-V semiconductors have a highly reactive surface and unlike SiO₂, the native oxides are complex in structure and composition leading to the formation of heavily defected interfaces that pin the semiconductor Fermi-level near midgap and degrades device performance. A significant effort has been focused on surface preparations prior to ALD that removes the native oxide and passivates the III-V atoms in order to ensure the best possible interface. Current approaches typically rely upon wet-chemical etches to remove the defect-prone native oxide layer prior to dielectric deposition; however, this technique typically suffers from a lack of reproducibility, as well as potential interface contamination between processing steps.

Recently, we demonstrated the use of an in situ hydrogen plasma treatment prior to the deposition of plasma enhanced ALD (PEALD) Al₂O₃ on GaSb. Samples demonstrating good electrical characteristics correlated to the elimination of Sb-oxide, a decrease in elemental Sb, as well as an increase in Ga₂O₃ as determined by XPS. While using plasma has been shown to produce good quality interfaces and subsequent dielectric films, a significant amount of surface roughening can take place across the semiconductor surface. Although surface roughness may not greatly influence the capacitance modulation of a MOS capacitor, it could significantly hamper charge mobility within a field-effect transistor (FET). Therefore, we investigated the surface roughness of a GaSb surface after exposure to hydrogen plasma as a function of select plasma parameters: rf-power, substrate temperature, and exposure time. Surfaces were characterized using atomic force microscopy, transmission electron microscopy, as well as, electrical measurements. Furthermore, we investigated the surface roughness across GaAs samples of different facets when exposed to a hydrogen plasma prior to PEALD in order to gain a better understanding of surface interactions during plasma assisted ALD.